feat: Initial metrics server

runtime/include/metrics_server.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include "tcp_server.h"
+
+extern struct tcp_server metrics_server;
+
+void metrics_server_init();
+int  metrics_server_listen();
+int  metrics_server_close();
+void metrics_server_handler(int client_socket);

runtime/src/listener_thread.c

@@ -5,6 +5,7 @@
 #include "global_request_scheduler.h"
 #include "generic_thread.h"
 #include "listener_thread.h"
+#include "metrics_server.h"
 #include "module.h"
 #include "runtime.h"
 #include "sandbox_functions.h"
@@ -134,6 +135,23 @@ listener_thread_register_tenant(struct tenant *tenant)
 	return rc;
 }
 
+int
+listener_thread_register_metrics_server()
+{
+	if (unlikely(listener_thread_epoll_file_descriptor == 0)) {
+		panic("Attempting to register metrics_server before listener thread initialization");
+	}
+
+	int                rc = 0;
+	struct epoll_event accept_evt;
+	accept_evt.data.ptr = (void *)&metrics_server;
+	accept_evt.events   = EPOLLIN;
+	rc = epoll_ctl(listener_thread_epoll_file_descriptor, EPOLL_CTL_ADD, metrics_server.socket_descriptor,
+	               &accept_evt);
+
+	return rc;
+}
+
 static void
 panic_on_epoll_error(struct epoll_event *evt)
 {
@@ -325,6 +343,29 @@ on_tenant_socket_epoll_event(struct epoll_event *evt)
 	}
 }
 
+static void
+on_metrics_server_epoll_event(struct epoll_event *evt)
+{
+	assert((evt->events & EPOLLIN) == EPOLLIN);
+
+	/* Accept Client Request as a nonblocking socket, saving address information */
+	struct sockaddr_in client_address;
+	socklen_t          address_length = sizeof(client_address);
+
+	/* Accept as many clients requests as possible, returning when we would have blocked */
+	while (true) {
+		int client_socket = accept4(metrics_server.socket_descriptor, (struct sockaddr *)&client_address,
+		                            &address_length, SOCK_NONBLOCK);
+		if (unlikely(client_socket < 0)) {
+			if (errno == EWOULDBLOCK || errno == EAGAIN) return;
+
+			panic("accept4: %s", strerror(errno));
+		}
+
+		metrics_server_handler(client_socket);
+	}
+}
+
 static void
 on_client_socket_epoll_event(struct epoll_event *evt)
 {
@@ -370,6 +411,10 @@ listener_thread_main(void *dummy)
 
 	generic_thread_initialize();
 
+	metrics_server_init();
+	metrics_server_listen();
+	listener_thread_register_metrics_server();
+
 	/* Set my priority */
 	// runtime_set_pthread_prio(pthread_self(), 2);
 	pthread_setschedprio(pthread_self(), -20);
@@ -390,7 +435,9 @@ listener_thread_main(void *dummy)
 		for (int i = 0; i < descriptor_count; i++) {
 			panic_on_epoll_error(&epoll_events[i]);
 
-			if (tenant_database_find_by_ptr(epoll_events[i].data.ptr) != NULL) {
+			if (epoll_events[i].data.ptr == &metrics_server) {
+				on_metrics_server_epoll_event(&epoll_events[i]);
+			} else if (tenant_database_find_by_ptr(epoll_events[i].data.ptr) != NULL) {
 				on_tenant_socket_epoll_event(&epoll_events[i]);
 			} else {
 				on_client_socket_epoll_event(&epoll_events[i]);

runtime/src/metrics_server.c

@@ -0,0 +1,67 @@
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "tcp_server.h"
+#include "http_total.h"
+
+struct tcp_server metrics_server;
+
+void
+metrics_server_init()
+{
+	tcp_server_init(&metrics_server, 1776);
+}
+
+int
+metrics_server_listen()
+{
+	return tcp_server_listen(&metrics_server);
+}
+
+int
+metrics_server_close()
+{
+	return tcp_server_close(&metrics_server);
+}
+
+void
+metrics_server_handler(int client_socket)
+{
+	int rc = 0;
+
+	char  *ostream_base = NULL;
+	size_t ostream_size = 0;
+	FILE  *ostream      = open_memstream(&ostream_base, &ostream_size);
+	assert(ostream != NULL);
+
+	uint32_t total_reqs = atomic_load(&http_total_requests);
+	uint32_t total_5XX  = atomic_load(&http_total_5XX);
+
+	fprintf(ostream, "HTTP/1.1 200 OK\r\n\r\n");
+
+	fprintf(ostream, "# TYPE total_requests counter\n");
+	fprintf(ostream, "total_requests: %d\n", total_reqs);
+
+	fprintf(ostream, "# TYPE total_rejections counter\n");
+	fprintf(ostream, "total_rejections: %d\n", total_5XX);
+	fflush(ostream);
+
+	rewind(ostream);
+
+	char   buf[256] = { 0 };
+	size_t nread    = 0;
+	do {
+		nread      = fread(buf, 1, 255, ostream);
+		buf[nread] = '\0';
+		/* TODO: Deal with blocking here! */
+		write(client_socket, buf, nread);
+	} while (nread > 0);
+
+	rc = fclose(ostream);
+	assert(rc == 0);
+
+	free(ostream_base);
+	ostream_size = 0;
+
+	close(client_socket);
+}